The patterns of evolution of pulmonary structural remodeling after experimental paraquat toxicity were studied in cynomolgous monkeys given 1 or 2 injections of 10 mg/kg of paraquat and sacrificed 2 days to 8 weeks later. Intraalveolar fibrosis was found to be more important than interstitial fibrosis in the structural remodeling that occurs in paraquat lung, because it results in obliteration of alveoli, coalescence of alveolat walls and loss of functional alveolar-capillary units.